ASSIGNMENT 8 keys
1. Knight 8.042. [370394] Show Details
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A house painter uses the chair and pulley arrangement of Figure P8.42 to lift himself up the side of a house. The painter's mass is 90 kg and the chair's mass is 10 kg. With what force must he pull down on the rope in order to accelerate upward at 0.16 m/s2?
[498] N
Figure P8.42
2. Knight 8.036. [455056] Show Details
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Figure P8.36 shows a block of mass m resting on a 20° slope. The block has coefficients of friction µs = 0.81 and µk = 0.40 with the surface. It is connected via a massless string over a massless, frictionless pulley to a hanging block of mass m2 = 2.0 kg.
Figure P8.36
(a) What is the minimum mass m that will stick and not slip?
[1.81] kg
(b) If this mimimum mass is nudged ever so slightly, it will start being pulled up the incline. What acceleration will it have?
[1.8] m/s2
3. Knight 8.032. [370391] Show Details
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The coefficient of static friction is 0.50 between the two blocks in Figure P8.32. The coefficient of kinetic friction between the lower block and the floor is 0.20. Force causes both blocks to cross a distance of 3.5 m, starting from rest. What is the least amount of time in which this motion can be completed without the top block sliding on the lower block?
[1.89] s
Figure P8.32
4. Knight 8.034. [455033] Show Details
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1.66
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1.66
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1.66
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1.66
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1.66
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1.7
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The 13.5 kg block in Figure P8.34 is held in place by the massless rope passing over two massless, frictionless pulleys. Find the following values.
Figure P8.34
tension T2 / [66.2] N
tension T3 / [66.2] N
tension T4 / [198] N
tension T5 / [66.2] N
the magnitude of force / [66.2] N
5. Knight 8.028. [488521] Show Details
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The lower block in Figure P8.28 is pulled on by a rope with a tension force of F = 27 N. The coefficient of kinetic friction between the lower block and the surface is 0.28. The coefficient of kinetic friction between the lower block and the upper block is also 0.28. What is the acceleration of the 2.0 kg block?
[4.43] m/s2
Figure P8.28
6. Knight 8.030. [370398] Show Details
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Mass m1 on the frictionless table of Figure P8.30 is connected by a string through a hole in the table to a hanging mass m2. With what speed must m1 rotate in a circle of radius r if m2 is to remain hanging at rest? (Express your answer using only m_1 for m1, m_2 for m2, r, and g for gravity.)
v = [sqrt((m_2 r g)/m_1)]
Figure P8.30
7. Knight 8.015. [370397] Show Details
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A mobile at the art museum has a 2.0 kg steel cat and 4.0 kg steel dog suspended from a lightweight cable, as shown in Figure Ex8.15. It is found that 1 = 20° when the center rope is adjusted to be perfectly horizontal. What are the tension and the angle of rope 3?
Figure Ex8.15
angle / [36.1]°
8. Knight 8.008. [455009] Show Details
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A 1100 kg car pushes a 2300 kg truck that has a dead battery. When the driver steps on the accelerator, the drive wheels of the car push against the ground with a force of 4600 N.
(a) What is the magnitude of the force of the car on the truck?
[3110] N
(b) What is the magnitude of the force of the truck on the car?
[3110] N
9. Knight 8.020. [493546] Show Details
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The sled dog in Figure P8.20 drags sleds A and B across the snow. The coefficient of friction between the sleds and the snow is 0.11. If the tension in rope 1 is 190 N, what is the tension in rope 2?
[342] N
Figure P8.20
10. Knight 8.025. [370389] Show Details
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Two packages at UPS start sliding down the 20° ramp shown in Figure P8.25. Package A has a mass of 4.0 kg and a coefficient of friction of 0.24. Package B has a mass of 10 kg and a coefficient of friction of 0.15. How long does it take package A to reach the bottom?
[1.52] s
Figure P8.25